Vibrating flow devices such as, for example, densitometers and Coriolis flow meters are used for measuring a characteristic of flowing substances, such as, for example, density, mass flow rate, volume flow rate, totalized mass flow, temperature, and other information. Vibrating flow devices include one or more conduits, which may have a variety of shapes, such as, for example, straight, U-shaped, or irregular configurations.
The one or more conduits have a set of natural vibration modes, including, for example, simple bending, torsional, radial, and coupled modes. The one or more conduits are vibrated by at least one drive at a resonance frequency in one of these modes for purposes of determining a characteristic of the flowing substance. One or more electronics transmit a sinusoidal drive signal to the at least one drive, which is typically a magnet/coil combination with the magnet typically being affixed to the conduit and the coil being affixed to a supporting structure or to another conduit. The drive signal causes the drive to vibrate the one or more conduits at the drive frequency in the drive mode. For example, the drive signal may be a periodic electrical current transmitted to the coil.
At least one pick-off detects the motion of a conduit and generates a sinusoidal pick-off signal representative of the motion of the vibrating conduit(s). The pick-off signal is transmitted to the one or more electronics; and according to well known principals the pick-off signal may be used by the one or more electronics to determine a characteristic of the flowing substance or adjust the drive signal, if necessary.
One problem that can occur in the data output from a vibrating flow device is an erroneous reading generated by sudden changes in the material. In particular, if the flowing substance is a liquid and there are particulates and/or gas bubbles in the liquid, this can cause large and inaccurate variations in the output.
The present invention is directed to overcoming this disadvantage inherent in prior vibrating flow devices.